1. Field of the Invention
The present invention relates to a magnetostatic wave device, and more particularly to a magnetostatic wave device comprising a magnetic garnet single crystal film.
2. Description of the Related Art
Single crystals of Y.sub.3 Fe.sub.5 O.sub.12 (referred to YIG hereinafter), a kind of magnetic garnet single crystal film, has been an important substance as a material for use in magnetostatic wave devices. A remarkable property of YIG is that it has an extremely small ferromagnetic half-width (.DELTA.H), which is related to the fact that the difference between input signals and output signals can be made small when it is used for the magnetostatic wave device. An additional feature is that a YIG is characterized by a saturation phenomenon at a relatively small input signal level. The YIG single crystal films have been widely used for magnetostatic wave devices such as limiters and noise filters by taking advantage of this phenomenon. Various kind of single crystal films of magnetic garnet containing iron have been also used for the magnetostatic wave device in addition to the YIG single crystal film described above.
However, the feature of the YIG output signal being saturated at a relatively small input signal level is not revealed immediately after receiving the input signal. Instead, the input signal is directly output as an output signal. There is therefore a transient response phenomenon in that the output signal is saturated as a function of a time lapse which causes a problem in that the function as a magnetostatic wave device can not be fully displayed. Although increasing the insertion loss of the magnetostatic wave device is one solution for this problem, too large an insertion loss makes the output signal level too small.